Optical printing of an originating color image borne on a transparent support onto a light sensitive color photographic display material can be accomplished by positioning the originating image between a light source and the light sensitive color photographic display material. Most generally, incandescent bulbs are employed as the light source for optical printing. Such incandescent bulbs are typically deficient in blue light relative to red or green light.
Light sensitive color photographic display materials such as color papers generally comprise a support bearing at least one red light-sensitive layer capable of forming a cyan colored image, at least one green light-sensitive layer capable of forming a magenta colored image and at least one blue light-sensitive layer capable of forming a yellow colored image, all as a result of appropriate chemical processing. These materials typically have a layer order such that a blue sensitive layer is further from an exposure source and closer to a support than other light sensitive layers. This layer order is dictated, inter alia, by the low acuity of the human eye to fine details in yellow images. Since the components in the overlying layers may scatter, reflect or absorb blue light, the blue light sensitive layer tends to receive less useful exposure than do overlying red or green light sensitive layers all other factors being equal.
Light sensitive color photographic originating materials, as typified by color negative films, comprise a support bearing at least one red light-sensitive layer capable of forming a cyan colored image, at least one green light-sensitive layer capable of forming a magenta colored image and at least one blue light-sensitive layer capable of forming a yellow colored image, all as a result of appropriate chemical processing. The chromogenic dyes formed in such a color film are far from perfected and exhibit undesired blue densities in addition to the desired red or green density. This limits the useful light available for exposure of the blue sensitive layer of a display material such as a color paper during a printing process.
Color negative films additionally incorporate integral color masking couplers, as described by Hanson and Vittum in the Photographic Society of America Journal, vol. 13, 94-ff (1947). Specifically, magenta dye-forming image couplers which release a yellow dye in an imagewise fashion while forming a magenta image dye may be employed in a green light sensitive layer of a color negative film to effectively reduce the imagewise formation of unwanted blue density in that layer while simultaneously providing a high but uniform blue density. Similarly, cyan dye-forming, yellow dye releasing masking couplers and so-called colorless or fugitive dye forming yellow dye releasing couplers are also known. While these masking couplers can improve system color reproduction by lowering the degree of undesired imagewise density formation in the color negative film, they inherently increase the blue density of a Dmin region of the color negative film. The result is that color reproduction can be improved but at a further cost in the useful blue exposure available to, for example, a color paper.
This situation is further complicated by the commercial need to maintain compatibility between different brands of color negative originating films, for example, and different offerings of these color films from a common manufacturer, at least when these films are intended for automated printing. Practically, this means that color negative films are formulated such that a camera normal exposure of a ca. 18% gray chart produces, after photographic processing, a fixed relationship between the red, green and blue densities that go into forming the image of this gray chart. The result of these practical constraints is that the individual color densities after a normal exposure and processing typically increase in the order red - green - blue, with blue the highest. This translates into the blue Dmin in a color negative film being highest and the blue transmission of the color negative being the smallest, all of which then places an even higher burden on the blue light sensitivity or speed of a color paper.
As a result of these factors the blue layer sensitivity of, for example, a color paper, dictates the overall useful sensitivity of such a photographic display material.
Attempts to remedy this difficulty by providing color display materials with higher blue sensitivity have generally proven unsuccessful. Although ever larger symmetric silver chloride and silver bromochloride may be precipitated and sensitized, these emulsions are known to gain little additional sensitivity with increased size, as has been reported by Farnell and Chanter in the Journal of Photographic Science, vol. 9, 73-ff (1961). An additional difficulty encountered with these symmetric emulsions, whatever their size, is a failure to show appropriately higher response as a function of increased exposure intensity, a problem known colloquially as High Intensity Reciprocity Failure (HIRF). This HIRF problem generally prevents achievement of meaningful improvements in printing time by increasing the intensity of the exposure source in a printing apparatus. Furthermore, these larger grains tend to exhibit poorer developability and covering power than the smaller grains thus limiting the optical density and the degree of color saturation that can be formed in the display material.
Recently, tabular shaped silver chloride emulsions have been reported by House et al at U.S. Pat. No. 5,320,938, and by Maskasky at U.S. Pat. No. 5,264,337 and U.S. Pat. No. 5,292,632. While these grains are said to provide improved sensitivity, there is little known about the specific use of such grains in color display materials, and no indication that these emulsions should specifically be employed in the blue light sensitive layer of a color display material in combination with specifically chosen spectral sensitizing dyes.